Eigenspectra of solar active region long-period oscillations G. Dumbadze, B. M. Shergelashvili, S. Poedts, T. V. Zaqarashvili, M. Khodachenko and P. De Causmaecker A&A, 653 (2021) A39 Published online: 06 September 2021 DOI: 10.1051/0004-6361/202038124